(a) Optimized crystal of the SARS-CoV nsp10–nsp16 complex. The scale bar is 100 µm in length. (b) NuPAGE analysis of the nsp10–nsp16 complex from optimized crystals. Ten optimized crystals were loaded onto a 4–12% NuPAGE gel and stained using Coomassie blue. Lane MK, molecular-weight markers; lane Xtal, nsp10–nsp16 complex. (c) X-ray diffraction pattern from a crystal of the SARS-CoV nsp16–nsp10 protein complex. Resolution arcs are shown. Reflections are observed to below 2 Å (an enlargement is shown in the inset).